The present invention pertains to medication dispensing devices, and, in particular, to a portable medication dispensing device such as an injector pen.
Patients suffering from a number of different diseases frequently must inject themselves with medication. To allow a person to conveniently and accurately self-administer medicine, a variety of devices broadly known as injector pens or injection pens have been developed. Generally, these pens are equipped with a cartridge including a piston and containing a multi-dose quantity of liquid medication. A drive member, extending from within a base of the injector pen and operably connected with typically more rearward mechanisms of the pen that control drive member motion, is movable forward to advance the piston in the cartridge in such a manner to dispense the contained medication from an outlet at the opposite cartridge end, typically through a needle that penetrates a stopper at that opposite end. In disposable or prefilled pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, a user, who then begins using a new replacement pen, discards the entire pen. In reusable pens, after a pen has been utilized to exhaust the supply of medication within the cartridge, the pen is disassembled to allow replacement of the spent cartridge with a fresh cartridge, and then the pen is reassembled for its subsequent use.
A number of known injection pens have utilized a mechanical advantage to facilitate operation. An injection pen disclosed in International Publication Number WO 96/26754 obtains a mechanical advantage with a gear set including first and second coaxial pinions that engage different racks within the pen, and which gear set travels with the pen thrust rod. Another injection pen with a mechanical advantage is disclosed in International Publication Number WO 01/95959, which pen uses one or more gear wheels carried by a connector element threadedly engaged with a piston rod. While these pens may be useful, their ability to provide high mechanical advantage may be limited by, for example, how small the gears can be made. In addition, these pens have relatively complicated designs, as well as potentially costly components, such as separate springs, which may undesirably impact the ability to effectively commercialize the pen in a disposable format.
Some other known injection pens that provide mechanical advantage have complicated designs that may make them relatively expensive to produce. Still another injection pen, such as disclosed in U.S. Pat. No. 5,938,642, is highly effective as a pre-filled device, but does not provide a mechanical advantage during injecting.
Thus, it would be desirable to provide an apparatus that can overcome one or more of these and other shortcomings of the prior art.